1. Field of the Invention
The present invention relates to a display device, which has a display panel, such as a liquid crystal panel, a PDP (Plasma Display Panel) or an organic EL (Electro-Luminescence), and which measures display characteristics (such as luminance or chromaticity) associated with display of the display panel.
2. Background Art
For example, a liquid crystal display device having a liquid crystal panel controls the transmittance amount of light from a backlight, which is provided on the back side thereof, by changing the light transmittance ratio of each pixel of the liquid crystal panel. Thus, the liquid crystal display device displays tone of the image. The light transmittance ratio of the liquid crystal panel may become off the designed values due to the manufacturing variations of the liquid crystal panel, and thereby the desired tone characteristics may not be obtained. For the countermeasure for the above, a memory may store an LUT (lookup table), which is associated with a tone level (tone value) based on a received image signal and an input level to the liquid crystal panel corresponding to the tone level. Then, the tone level is converted into the input level based on the LUT for correcting the unique tone characteristics of each display device in order to achieve desired tone characteristics.
However, characteristics of the liquid crystal panel and the backlight may change across the ages during the usage of the display device. When the aging occurs, it may be impossible to achieve the desired tone characteristics even after the correction of the tone characteristics based on the LUT stored during the production or the shipping of the display device. It is possible to deal with the above problem if the user updates the LUT (or performs the calibration) after the shipping of the display device. Since it is necessary to measure the actual display characteristics of the display device during the execution of the calibration, the display device is provided with a sensor for the measurement. FIGS. 10(a) to 10(c) are schematic diagrams for explaining methods for measuring the display characteristics in conventional display devices.
For example, a conventional display device is configured to have a light sensor provided in the vicinity of the backlight within the display device, and is configured to execute the calibration based on the luminance of the backlight measured by the light sensor (not shown in FIGS. 10(a) to 10(c)). However, the light sensor of the display device is only capable of measuring characteristics of the backlight, and thereby it is disadvantageously not possible to execute the calibration in consideration of the characteristics of the liquid crystal panel.
Also, for example, another display device is configured to have a separate light sensor used for measuring the display characteristics (see FIG. 10(a)). When the display device is used for the measurement, the user is required to connect the light sensor with the display device through a cable and the like, and to attach the light sensor to a suitable position (such as a center position) on the screen of the liquid crystal panel. In this configuration with the separate light sensor, since it is possible to measure the display characteristics based on the image displayed on the liquid crystal panel, it is advantageously possible to measure the display characteristics for not only the backlight, but also for the liquid crystal panel. However, it is a problem that the user himself/herself has to take time to install the light sensor for the calibration. Also, since the center of the screen is covered by the light sensor, there is another problem that the user is incapable of using the display device during the measurement of the display characteristics.
Also, for example, there is still another display device that has a movable light sensor (hereinafter referred to as a swing sensor) (see FIG. 10(b)). The swing sensor is attached to a framing member that surrounds the liquid crystal panel, and is extendable over the screen by a motor, an actuator, or the like. Furthermore, there is further another display device configured to have a swing sensor that is built in the framing member of the display device (see FIG. 10(c)). The above display devices are advantageously capable of measuring the display characteristics of the backlight and the liquid crystal panel, and allow the user to operate the display devices with the swing sensor mounted thereon. Since the display devices are configured such that the light sensor is movable to cover the peripheral part of the screen only when the display characteristics are measured, it is possible to solve the problem of taking time for the measurement of the display characteristics. Also, the user is allowed to use the display device even when the display characteristics are measured since the light sensor is configured to cover only a part of the peripheral part of the screen.
Also, Patent Document 1 proposes a liquid crystal display device that has a detecting pattern drawn in an invisible area of liquid crystal display plate, and a light detection sensor is provided at the pattern position. The light detection sensor detects transmitted light from a backlight, which is provided at a back side of the liquid crystal display plate, and automatically controls bias voltage, which is sent to an image control unit of the liquid crystal display plate to maximize the contrast of the detecting pattern. As a result, the liquid crystal display device is capable of reliably and automatically adjusting the contrast of the liquid crystal display plate regardless of the particular difference of various characteristics of each product.
Patent Document 2 proposes a display device that is provided with a light sensor having a light receiving surface. The light receiving surface is tilted relative to a light guiding hole, which is formed at a side of a reflecting plate that reflects light of a backlight, and to a front face of the display device by a predetermined angle such that the light receiving surface receives light through the light guiding hole and extraneous light from the exterior of the device. The display device is configured to switch the luminance of the backlight based on the light receiving results of the light sensor. Thus, the display device is capable of preventing frequent switching of the luminance of the backlight due to a slight change of the extraneous light.